release: 1.3.118

[lilypond.git] / Documentation / user / refman.itely

@c -*-texinfo-*-
@c TODO: 
@c - Reinsert subsection commands that were lost in the
@c   ancient conversion from YODL!  /MB
@c - Restructure! Separate internal commands from user level commands. /MB
@c - Add some words about Guile.  /MB
@c - Fix indexing (keyindex) so it doesn't add line breaks  /MB

@node Reference Manual, ,  , Top
@chapter Reference Manual

@menu
* Overview::                       Overview
* Top level::                      Top level
* Pitch names::                    Pitch names
* Lexical conventions::            Lexical conventions
* Other languages::                Note names in various languages
* Lexical modes::                          modes
* Types::                          Types
* Music expressions::              Music expressions
* Atomic music expressions::       Atomic music expressions
* Note specification::             notedesc
* barlines::                       barlines
* Manual beams::                   Manual beam
* stem tremolo::                   tremolo
* Compound music expressions::     Compound music expressions
* relative::                       relative
* Repeats::                        Repeats      
* transpose::                      transpose
* Ambiguities::                    Ambiguities
* Notation conversion specifics::  Notation conversion specifics
* autobeam::                       autobeam
* lyricprint::                     lyricprint
* Notation Contexts::              Notation Contexts
* Properties::                     Changing formatting
* Notation output definitions::    Notation output definitions
* paper::                          paper
* Paper variables::                papervars
* contextdefs::                    contextdefs
* Sound output::                   Sound output
* midilist::                       midilist
* Grobs::                          Graphical objects
* Molecule::                       Molecules
* Pre-defined Identifiers::        Pre-defined Identifiers
@c May be fragile.  Better make single link to generated doco?
* Interpretation contexts:(lilypond-internals)LilyPond interpretation contexts.
* Engravers:(lilypond-internals)LilyPond engravers.
* Backend:(lilypond-internals)LilyPond backend.
@end menu



@node Overview, , , Reference Manual
@section Overview

This document@footnote{This document has been revised for LilyPond 1.2.}
describes the the GNU LilyPond input format This format represents a
piece of music in an elegant way, but contains enough information for
both automatic typesetting and automatic performances.

LilyPond input can be classified  into three types:
@itemize @bullet
  @item musical expressions: a musical expression is some combination of
rest, notes, lyrics
  @item output definitions: recipes for translating those musical
expressions into performances (MIDI) or graphics (eg. PostScript).

  @item declarations: by declaring and naming musical expressions, you
can enter and edit them in manageable chunks.
@end itemize



@node Top level, , , Reference Manual
@section Top level

@cindex top level

This section describes what you may enter at top level.



@cindex score definition

The output is generated combining a music expression with an output
definition.  A score block has the following syntax:

@example
  \score @{ @var{musicexpr} @var{outputdefs} @}
@end example

@var{outputdefs} are zero or more output definitions.  If no output
definition is supplied, the default @code{\paper} block will be added.

@cindex header

@keyindex{header}

The syntax is

@example
  \header @{ @var{key1} = @var{val1};
             @var{key2} = @var{val2}; @dots{} @}
@end example

A header describes the file's contents.  It can also appear in a
@code{\score} block.  Tools like @code{ly2dvi}@indexcode{ly2dvi} can use this
information for generating titles.  Key values that are used by
@code{ly2dvi} are: title, subtitle, composer, opus, poet, instrument,
metre, arranger, piece and tagline.

It is customary to put the @code{\header} at the top of the file.


@node Pitch names, , ,  Reference Manual

Note names and chord modifiers can be customised for nationalities.
languages and conventions.  The syntax is as follows.
@example
   \pitchnames @keyindex{pitchnames} @var{scheme-alist}
   \chordmodifiers@keyindex{chordmodifiers} @var{scheme-alist}
@end example

See @file{ly/nederlands.ly} and @file{ly/chord-modifiers.ly} for
specific examples how to do this.  tables can be tailored specified
using. Some national note names have been provided, see @ref{Other
languages}.

A @code{\paper} block at top level sets the default paper block.  A
@code{\midi} block at top level works similarly.



Identifier assignments may appear at top level.  Semicolons are
forbidden after top level assignments.



@node Lexical conventions, , ,  Reference Manual
@section Lexical conventions

@cindex lexical conventions



@unnumberedsubsec Comments

@cindex comment

@indexcode{%}


A one line comment is introduced by a `@code{%}' character. 
Block comments are started by `@code{%@{}' and ended by `@code{%@}}'. 
They cannot be nested.

@unnumberedsubsec Scheme

@indexcode{#}

LilyPond contains a Scheme interpreter (the GUILE library) for
internal use. The interpreter is accessed by the pound sign:

Whereever the syntax allows Scheme expressions, you may enter one as

@example
  #@var{scheme}
@end example

Evaluates the specified Scheme code. If this is used at toplevel, then
the result is discarded. Example:
@example
  \property Staff.TestObject \override #'symbol =  #(+ 1 2)
@end example

(in this case, @code{\override} expects two Scheme expressions. 

[refer appendix/ online intro on Scheme] 

@unnumberedsubsec Keywords

@cindex keyword

Keywords start with a backslash, followed by a number of lower case
alphabetic characters.  These are all the keywords.

@example
apply arpeggio autochange spanrequest commandspanrequest
simultaneous sequential accepts alternative bar breathe
char chordmodifiers chords clef cm consists consistsend
context denies duration dynamicscript elementdescriptions
font grace header in lyrics key mark musicalpitch
time times midi mm name pitchnames notes outputproperty
override set revert partial paper penalty property pt
relative remove repeat addlyrics partcombine score
script stylesheet skip textscript tempo translator
transpose type
@end example

@unnumberedsubsec Integers

@cindex integer

Formed from an optional minus sign followed by digits.  Arithmetic
operations cannot be done with integers, and integers cannot be mixed
with reals.

@unnumberedsubsec Reals

@cindex real
 

Formed from an optional minus sign and a sequence of digits followed
by a @emph{required} decimal point and an optional exponent such as
@code{-1.2e3}.  Reals can be built up using the usual operations:
`@code{+}@indexcode{+}', `@code{-}@indexcode{-}', `@code{*}@indexcode{*}', and
`@code{/}@indexcode{/}', with parentheses for grouping.

A real constant can be followed by one of the dimension
keywords:
@cindex dimensions
 @code{\mm}@keyindex{mm},
@code{\pt}@keyindex{pt}, @code{\in}@keyindex{in}, or
@code{\cm}@keyindex{cm}, for millimeters, points, inches and
centimeters, respectively.  This converts the number to a real that
is the internal representation of dimensions.


@unnumberedsubsec
@cindex string
 
Begins and ends with the `@code{"}' character.  To include a `@code{"}'
character in a string write `@code{\"}'.  Various other backslash
sequences have special interpretations as in the C language.  A string
that contains no spaces can be written without the quotes.  See
@ref{Lexical modes} for details on unquoted strings; their interpretation varies
depending on the situation.  Strings can be concatenated with the
`@code{+}' operator.

The tokenizer accepts the following commands. They have no grammatical
function, hence they can appear anywhere in the input.

@example
  \maininput@keyindex{maininput}
@end example

This command is used in init files to signal that the user file must
be read. This command cannot be used in a user file.

@unnumberedsubsec file inclusion

@example
  \include@keyindex{include} @var{file}
@end example

Include @var{file}.  The argument @var{file} may be a quoted string (an
unquoted string will not work here!) or a string identifier.  The full
filename including the @file{.ly} extension must be given,

@unnumberedsubsec Version information 

@example
  \version@keyindex{version} @var{string} ;
@end example

Specify the version of LilyPond that a file was written for.  The
argument is a version string in quotes, for example @code{"1.2.0"}. 
This is used to detect invalid input, and to aid
@code{convert-ly}, a tool that automatically upgrades input files.



@cindex other languages

@node Other languages, , ,  Reference Manual

Note name definitions have been provided in various languages. 
Simply include the language specific init file.  For example:
`@code{\include "english.ly"}'.  The available language files and the
names they define are:

@example 
                        Note Names               sharp       flat
nederlands.ly  c   d   e   f   g   a   bes b   -is         -es
english.ly     c   d   e   f   g   a   bf  b   -s/-sharp   -f/-flat
deutsch.ly     c   d   e   f   g   a   b   h   -is         -es
norsk.ly       c   d   e   f   g   a   b   h   -iss/-is    -ess/-es
svenska.ly     c   d   e   f   g   a   b   h   -iss        -ess
italiano.ly    do  re  mi  fa  sol la  sib si  -d          -b
catalan.ly     do  re  mi  fa  sol la  sib si  -d/-s       -b 
@end example 

Pitch names can be redefined using the @code{\pitchnames} command, see
@ref{Pitch names}.

@cindex Lexical Modes

@cindex modes

@node Lexical modes, , ,  Reference Manual

To simplify entering notes, lyrics, and chords, @emph{Lilypond} has three
special input modes on top of the default mode.  In each mode, words
are identified on the input.  If @code{"word"} is encountered, it is
treated as a string.  If @code{\word} is encountered, it is treated as
a keyword or as an identifier.  The behavior of the modes differs in
two ways: Different modes treat unquoted words differently, and
different modes have different rules for deciding what is a word.

@table @samp
  @item Normal mode.
@cindex mode!normal
 
    At the start of parsing, @emph{Lilypond} is in Normal mode.  In Normal
    mode, a word is an alphabetic character followed by alphanumeric
    characters.  If @code{word} is encountered on the input it is
    treated as a string.

  @item Note mode.
@cindex mode!note

    Note mode is introduced by the keyword
    @code{\notes}@keyindex{notes}.  In Note mode, words can only
    contain alphabetic characters.  If @code{word} is encountered,
    LilyPond first checks for a notename of @code{word}.  If no
    notename is found, then @code{word} is treated as a string.

    Since combinations of numbers and dots are used for indicating
    durations, it is not possible to enter real numbers in this mode.

  @item Chord mode.
@cindex mode!chord

    Chord mode is introduced by the keyword
    @code{\chords}@keyindex{chords}.  It is similar to Note mode, but
    words are also looked up in a chord modifier table (containing
    @code{maj}, @code{dim}, etc).

    Since combinations of numbers and dots are used for indicating
    durations, you can not enter real numbers in this mode.  Dashes
    and carets are used to indicate chord additions and subtractions,
    so scripts can not be entered in Chord mode.

  @item Lyrics mode. 
@cindex mode!lyric

    Lyrics mode is introduced by the keyword
    @code{\lyrics}@keyindex{lyrics}.  This mode has rules that make it
    easy to include punctuation and diacritical marks in words.  A
    word in Lyrics mode begins with: an alphabetic character,
    `@code{_}', `@code{?}', `@code{!}', `@code{:}', `@code{'}', the
    control characters @code{^A} through @code{^F}, @code{^Q} through
    @code{^W}, @code{^Y}, @code{^^}, any 8-bit character with ASCII code
    over 127, or a two-character combination of a backslash followed
    by one of `@code{`}', `@code{'}', `@code{"}', or
    `@code{^}'.@footnote{The purpose of Lyrics mode is that you can
    enter lyrics in @TeX{} format or a standard encoding without
    needing quotes.  The precise definition of this mode indeed is
    ludicrous.  This will remain so until the authors of LilyPond
    acquire a deeper understanding of character encoding, or someone
    else steps up to fix this.}

    Subsequent characters of a word can be any character that is not
    a digit and not white space.  One important consequence of this
    is that a word can end with `@code{@}}', which may be confusing if
    you thought the closing brace was going to terminate Lyrics
    mode.@footnote{LilyPond will issue a warning, though.}  Any
    `@code{_}' character which appears in an unquoted word is
    converted to a space.  This provides a mechanism for introducing
    spaces into words without using quotes.  Quoted words can also be
    used in Lyrics mode to specify words that cannot be written with
    the above rules.  Here are some examples.  Not all of these words
    are printable by @TeX{}.

@example 
Ah!             % a word
2B_||_!2B       % not a word because it starts with a digit
``Hello''       % not a word because it starts with `
_ _ _ _         % 4 words, each one a space 
@end example 

    Since combinations of numbers and dots are used for indicating
    durations, you can not enter real numbers in this mode.
@end table

[todo: include short table showign differences] 

@node Types, , ,  Reference Manual
@section Types

@cindex  Identifiers

[say something about types]

All of the information in a LilyPond input file, is represented as a
Scheme value. In addition to normal Scheme data types (such as pair,
number, boolean, etc.), LilyPond has a number of specialized data types,

@itemize @bullet
  @item Input
  @item c++-function
  @item Music: see @ref{Music expressions}
  @item Identifier
  @item Translator_def:
See section @ref{contextdefs} for more information

  @item Duration
  @item Pitch
  @item Score
  @item Music_output_def (TODO: this is not really a Scheme object
yet. Nevertheless, you can use identifiers to make references to them )
  @item Moment (rational number)
@end itemize

LilyPond also includes some transient object types. Objects of these
types are built during a LilyPond run, and do not `exist' per se within
your input file. These objects are created as a result of your input
file, so you can include commands in the input to manipulate them,
during a lilypond run.

@itemize @bullet
  @item Grob: short for Graphical object. See @ref{Grobs}. 
  @item Molecule: device-independent page output object,
    including dimensions.  Produced by some Grob functions
    See @ref{Molecules}
  @item Translator: object that produces audio objects or Grobs.
  @item Font_metric: object representing a font. (Not yet user
accessible.)

@c  @item Audio_element: (todo,  smobme)
@end itemize

Identifiers allow objects to be assigned to names during the parse
stage.  To assign an identifier, you use `@var{name}=@var{value}' and to
refer to an identifier, you preceed its name with a backslash:
`@code{\}@var{name}'.  Identifier assignments must appear at top level
in the @emph{Lilypond} file.  Semicolons are forbidden after assignments
appearing at top level but they are obligatory after assignments
appearing in the @code{\paper} block, see Section @ref{paper}.

@var{value} is any valid Scheme value or any of the input-types listed
above.

An identifier can be created with any string for its name, but you will
only be able to refer to identifiers whose names begin with a letter,
being entirely alphanumeric.  It is impossible to refer to an identifier
whose name is the same as the name of a keyword.

The right hand side of an identifier assignment is parsed completely
before the assignment is done, so it is allowed to redefine an
identifier in terms of its old value, e.g.

@example
  foo = \foo * 2.0
@end example

When an identifier is referenced, the information it points to is
copied.  For this reason, an identifier reference must always be the
 first item in a block.
@example
\paper  @{
   foo = 1.0
   \paperIdent % wrong and invalid
@}

\paper @{
   \paperIdent % correct
   foo = 1.0
@}
@end example


@node Music expressions, , ,  Reference Manual
@section Music expressions

@cindex music expressions

Music in @emph{Lilypond} is entered as a music expression.  Notes, rests,
lyric syllables are music expressions (the atomic
expressions)
@cindex atomic music expressions
, and you can combine
music expressions to form new ones.  This example forms a compound
expressions out of the quarter @code{c} note and a @code{d}
note:

@example 
\sequential @{ c4 d4 @} 
@end example 

The meaning of this compound expression is to play the `@code{c}'
first, and then the `@code{d}' (as opposed to playing them
simultaneously, for instance).

Atomic music expression are discussed in
subsection @ref{Atomic music expressions}.  Compound music expressions are
discussed in subsection @ref{Compound music expressions}.



@node Atomic music expressions, , ,  Reference Manual
@section Atomic music expressions




@cindex pitch

@cindex duration
 

The syntax for pitch specification is


@example
  \musicalpitch@keyindex{musicalpitch} @{ @var{octave} @var{note} @var{shift} @}
@end example

@var{octave} is specified by an integer, zero for the octave
containing middle C.  @var{note} is a number from 0 to 7, with 0
corresponding to C and 7 corresponding to B.  The shift is zero for a
natural, negative to add flats, or positive to add sharps.

In Note and Chord mode, pitches may be designated by names.  See
section @ref{Other languages} for pitch names in different languages.

The syntax for duration specification is

@example
 \duration@keyindex{duration}
   @{ @var{length} @var{dotcount} @}
@end example

@var{length} is the negative logarithm (base 2) of the duration:
1 is a half note, 2 is a quarter note, 3 is an eighth
note, etc.  The number of dots after the note is given by
@var{dotcount}.

In Note, Chord, and Lyrics mode, durations may be designated by
numbers and dots.  


@node Note specification, , ,  Reference Manual

@cindex note specification

@cindex pitches

@cindex entering notes

A note specification has the form

@example
  @var{pitch}[@var{octavespec}][!][?][@var{duration}]
@end example

The pitch of the note is specified by the note's name.


The default names are the Dutch note names.  The notes are specified
by the letters `@code{c}' through `@code{b}', where `@code{c}' is an
octave below middle C and the letters span the octave above that C. 
In Dutch,
@cindex notenames!Dutch
a sharp is formed by adding `@code{-is}' to the end of a pitch name.  A
flat is formed by adding `@code{-es}'. Double sharps and double flats
are obtained by adding `@code{-isis}' or `@code{-eses}'.  `@code{aes}'
and `@code{ees}' are contracted to `@code{as}' and `@code{es}' in Dutch,
but both forms will be accepted.

LilyPond has predefined sets of notenames for various languages.  See
@ref{Other languages}.



The optional octave specification takes the form of a series of
single quote (`@code{'}@indexcode{'}') characters or a series of comma
(`@code{,}@indexcode{,}') characters.  Each @code{'} raises the pitch by one
octave; each @code{,} lowers the pitch by an octave.

@lilypond[fragment,verbatim,center]
  c' d' e' f' g' a' b' c''
@end lilypond

@lilypond[fragment,verbatim,center]
  cis' dis' eis' fis' gis' ais' bis'
@end lilypond

@lilypond[fragment,verbatim,center]
  ces' des' es' fes' ges' as' bes'
@end lilypond

@lilypond[fragment,verbatim,center]
  cisis' eisis' gisis' aisis' beses'
@end lilypond

@lilypond[fragment,verbatim,center]
  ceses' eses' geses' ases' beses'
@end lilypond

Whenever a C-sharp is desired,  you must specify a C-sharp.  LilyPond
will determine what accidentals to typeset depending on the key and
context.  A reminder accidental 
@cindex reminder accidental
 can be
forced by adding an exclamation mark `@code{!}' after the pitch.  A
cautionary accidental, 
@cindex cautionary accidental
 i.e., an
accidental within parentheses can be obtained by adding the question
mark `@code{?}@indexcode{?}' after the pitch.

@lilypond[fragment,verbatim,center]
  cis' d' e' cis'  c'? d' e' c'!
@end lilypond


@cindex duration

Durations are entered as their reciprocal values.  For notes longer
than a whole note, use identifiers.

@quotation

@example 
c'\longa c'\breve  
c'1 c'2 c'4 c'8 c'16 c'32 c'64 c'64 
@end example 

@end quotation

@quotation

@lilypond[]
\score {
  \notes \relative c'' {
    a\longa a\breve  
    a1 a2 a4 a8 a16 a32 a64 a64 
  }
  \paper {
%{    \translator {
      \StaffContext
        \remove "Clef_engraver";
        \remove "Staff_symbol_engraver";
    } %}
  }
}
@end lilypond
@end quotation

@quotation

@example 
r\longa r\breve  
r1 r2 r4 r8 r16 r32 r64 r64 
@end example 

@end quotation

@quotation

@lilypond[]
\score {
  \notes \relative c'' {
    r\longa r\breve  
    r1 r2 r4 r8 r16 r32 r64 r64 
  }
  \paper {
    loose_column_distance = 2.5 * \staffspace;
    linewidth = -1.0;
    \translator {
        \StaffContext
        \remove "Clef_engraver";
        \remove "Staff_symbol_engraver";
        \remove "Bar_engraver";
    }
  }
}
@end lilypond
@end quotation

If the duration is omitted then it is set equal to the previous
duration.  If there is no previous duration, a quarter note is
assumed.  The duration can be followed by a dot (`@code{.}@indexcode{.}')
to obtain dotted note lengths.

@lilypond[fragment,verbatim,center]
  a'4. b'4.
@end lilypond

You can alter the length of duration by writing
`@code{*}@var{fraction}' after it.  This will not affect the
appearance of note heads or rests.


Rests are entered like notes, with note name `@code{r}@indexcode{r}',
or `@code{R}@indexcode{R}'.  There is also a note name
`@code{s}@indexcode{s}', which produces a space of the specified
duration.  `@code{R}' is specifically meant for entering parts: the
@code{R} rest can expand to fill a score with rests, or it can be
printed as a single multimeasure rest.

You can control the expansion by setting the property
@code{Score.skipBars}. If this is set to true, Lily will not expand
empty measures, and the multimeasure rests automatically adds the
appropriate number.


@cindex lyrics expressions

Syllables are entered like notes, with pitches replaced by text.  For
example, `@code{Twin-4 kle4 twin-4 kle4}' enters four syllables, each
with quarter note duration.  Note that the hyphen has no special
meaning for lyrics, and does not introduce special symbols.  See
section @ref{Lexical modes} for a description of what is interpreted as
lyrics.

Spaces can be introduced into a lyric either by using quotes
(`@code{"}') or by using an underscore without quotes: `@code{He_could4
not4}'.  All unquoted underscores are converted to spaces.  Printing
lyrics is discussed in section @ref{lyricprint}.



@cindex properties

@example
  \property@keyindex{property}
    @var{contextname}.@var{propname} =  @var{value}
@end example

Sets the @var{propname} property of the context @var{contextname} to
the specified @var{value}.  All three arguments are strings. 
Depending on the context, it may be necessary to quote the strings or
to leave space on both sides of the dot.



@cindex translator switches

@example
  \translator@keyindex{translator}
    @var{contexttype} = @var{name}
@end example

A music expression indicating that the context which is a direct
child of the a context of type @var{contexttype} should be shifted to
a context of type @var{contexttype} and the specified name.

Usually this is used to switch staffs in Piano music, e.g.

@example
  \translator Staff = top @var{Music}
@end example


@cindex output properties


These allow you to tweak what is happening in the back-end
directly. If you want to control every detail of the output
formatting, this is the feature to use. The downside to this is that
you need to know exactly how the backend works. Example:


@lilypond[fragment,verbatim]
\relative c'' { c4
        \context Staff \outputproperty
                #(make-type-checker 'Note_head)
                #'extra-offset = #'(5.0 . 7.5)
<c8 e g> }
@end lilypond

This selects all note heads occurring at current staff level, and sets
the extra-offset of those heads to (5,7.5), shifting them up and
right.

Use of this feature is entirely on your own risk: if you use this, the
result will depend very heavily on the implementation of the backend,
which we change regularly and unscrupulously.


@cindex commands

Commands are music expressions that have no duration.   


@example

  @code{\key}@keyindex{key} @var{pitch} @var{type} @code{;}
@end example

Change the key signature.  @var{type} should be
@code{\major}@keyindex{major} or @code{\minor}@keyindex{minor} to get
@var{pitch}-major or @var{pitch}-minor, respectively.  The second
argument is optional; the default is major keys.  The @var{\context}
argument can also be given as an integer, which tells the number of
semitones that should be added to the pitch given in the subsequent
@code{\key}@keyindex{key} commands to get the corresponding major key,
e.g., @code{\minor}@keyindex{minor} is defined as 3.  The standard
mode names @code{\ionian}@keyindex{ionian},
@code{\locrian}@keyindex{locrian}, @code{\aeolian}@keyindex{aeolian},
@code{\mixolydian}@keyindex{mixolydian}, @code{\lydian}@keyindex{lydian},
@code{\phrygian}@keyindex{phrygian}, and @code{\dorian}@keyindex{dorian}
are also defined.

@example
  @code{\keysignature}@keyindex{keysignature} @var{pitchseq} @code{;}
@end example

Specify an arbitrary key signature.  The pitches from @var{pitch} will
be printed in the key signature in the order that they appear on the
list.
        
@example
  \mark@keyindex{mark} @var{unsigned};
  \mark @var{string};
@end example

Prints a mark over or under the staff.  You must add
@code{Mark_engraver}@indexcode{Mark_engraver} to the Score context for
this to work.

@node barlines, , ,  Reference Manual

@example
  \bar@keyindex{bar} @var{bartype};
@end example

This is a short-cut for doing
@example
  \property Score.whichBar = @var{bartype} 
@end example

You are encouraged to use @code{\repeat} for repetitions.  See 
@ref{Repeats}, and the documentation of @code{whichBar}.


@example
  \time@keyindex{time} @var{numerator}@code{/}@var{denominator} @code{;}
@end example

A short-cut for doing
@example
     \property Score.timeSignatureFraction = #'(@var{numerator} . @var{denominator})
@end example

See the documentation of @code{timeSignatureFraction}

@example

  \tempo@keyindex{tempo} @var{duration} = @var{perminute} @code{;}
@end example

Used to specify the tempo.  For example, `@code{\tempo 4 = 76;}'
requests output with 76 quarter notes per minute.

@example
  \partial@keyindex{partial} @var{duration} @code{;}
@end example

Short cut for 

@example
  \property Score.measurePosition = @var{length of duration}
@end example

See the documentation of @code{measurePosition}.

@cindex anacrusis

@cindex upstep

@example

  @code{|}@indexcode{|}
@cindex bar check

@end example

@cindex shorten measures

@cindex upstep

`@code{|}' is a bar check.  Whenever a bar check is encountered during
interpretation, a warning message is issued if it doesn't fall at a
measure boundary.  This can help you finding errors in the input.
Depending on the value of @code{barCheckNoSynchronize}
@indexcode{barCheckNoSynchronize} The beginning of the measure will be
relocated, so this can also be used to shorten measures.


@example

  \penalty@keyindex{penalty} @var{int} @code{;}
@end example

Discourage or encourage line breaks.  See identifiers
@code{\break}@keyindex{break} and @code{\nobreak}@keyindex{nobreak} in
section [on identifiers] [FIXME].

@example
  \clef@keyindex{clef} @var{clefname} @code{;}
@end example

Short-cut for

@example
  \property Clef.clefGlyph = @var{symbol associated with clefname} 
  \property Clef.clefPosition = @var{clef Y-position for clefname}
  \property Clef.clefOctavation = @var{extra pitch of clefname}
@end example

Supported clef-names include 

[todo]

@example

  \skip@keyindex{skip} @var{duration} @code{;}
@end example

Skips the amount of time specified by @var{duration}.  If no other
music is played, a gap will be left for the skipped time with no
notes printed.  It works in Note Mode or Lyrics Mode.  In Note mode,
this has the same effect as the space rest `@code{s}'.


@cindex beams

@node Manual beams, , ,  Reference Manual

A beam is specified by surrounding the beamed notes with brackets
`@code{[}@indexcode{[}' and `@code{]}@indexcode{]}'.  

@lilypond[fragment,verbatim,center]
  [a'8 a'] [a'16 a' a' a']
@end lilypond

Some more elaborate constructions:

@lilypond[fragment,verbatim,center]
  [a'16 <a' c''> c'' <a' c''>]
  \times 2/3 { [e'8 f' g'] }
@end lilypond

Beaming can be generated automatically; see section @ref{autobeam}.

[OUTDATED, FIXME]

To place tremolo marks between notes, use @code{\repeat} with tremolo
style.
@cindex tremolo beams
To create tremolo beams on a single note, simply attach
`@code{:}@var{length}' to the note itself.

@lilypond[fragment,verbatim,center]
  \repeat "tremolo" 8 { c16 d16 }
  \repeat "tremolo" 4 { c16 d16 }    
@end lilypond

@lilypond[fragment,verbatim,center]
  c'4:32
@end lilypond


@cindex --@@@code{-}@code{-}

@indexcode{__}

@cindex extender

@cindex hyphen

The syntax for an extender mark is `@code{__}'.  This syntax can only
be used within lyrics mode.  The syntax for a spanning hyphen (i.e.,
a hyphen that will be printed between two lyric syllables) is
`@code{-}@code{-}'.


@cindex ties

A tie connects two adjacent note heads of the same pitch.  When used
with chords, it connects all of the note heads whose pitches match.
Ties are indicated using the tilde symbol `@code{~}@indexcode{~}'.
If you try to tie together chords which have no common pitches, a
warning message will appear and no ties will be created.

@lilypond[fragment,verbatim,center]
  e' ~ e' <c' e' g'> ~ <c' e' g'>
@end lilypond



[TODO: explain Requests]


@cindex articulations

@cindex scripts

@cindex ornaments

A variety of symbols can appear above and below notes to indicate
different characteristics of the performance.  These symbols can be
added to a note with `@var{note}@code{-\}@var{name}'.  Numerous symbols
are defined in @file{script.ly} and @file{script.scm}.  Symbols can be
forced to appear above or below the note by writing
`@var{note}@code{^\}@var{name}' and `@var{note}@code{_\}@var{name}'
respectively.  Here is a chart showing symbols above notes, with the
name of the corresponding symbol appearing underneath.

@lilypond[]

  \score {
    < \notes {
        c''-\accent      c''-\marcato      c''-\staccatissimo c''-\fermata 
        c''-\stopped     c''-\staccato     c''-\tenuto        c''-\upbow
        c''-\downbow     c''^\lheel        c''-\rheel         c''^\ltoe
        c''-\rtoe        c''-\turn         c''-\open          c''-\flageolet
        c''-\reverseturn c''-\trill        c''-\prall         c''-\mordent
        c''-\prallprall  c''-\prallmordent c''-\upprall       c''-\downprall
        c''-\thumb       c''-\segno        c''-\coda
      }
      \context Lyrics \lyrics {  
        accent__      marcato__      staccatissimo__ fermata
        stopped__     staccato__     tenuto__        upbow
        downbow__     lheel__        rheel__         ltoe
        rtoe__        turn__         open__          flageolet
        reverseturn__ trill__        prall__         mordent
        prallprall__  prallmordent__ uprall__        downprall
        thumb__       segno__        coda
      }
    >
    \paper {
      linewidth = 5.875\in;          
      indent    = 0.0;
    }
  }

@end lilypond

In addition, it is possible to place arbitrary strings of text or
@TeX{} above or below notes by using a string instead of an
identifier: `@code{c^"text"}'.  Fingerings 
@cindex fingering
 can be
placed by simply using digits.  All of these note ornaments appear in
the printed output but have no effect on the MIDI rendering of the
music.

To save typing, fingering instructions (digits 0 to 9 are
supported) and single characters shorthands exist for a few
common symbols

@lilypond[]

  \score {
    \notes {
      \property Voice.textStyle = typewriter
      c''4-._"c-."      s4
      c''4--_"c-{}-"    s4
      c''4-+_"c-+"      s4
      c''4-|_"c-|"      s4
      c''4->_"c->"      s4
      c''4-^_"c-\\^{ }" s4
      c''4-1_"c-1"      s4
      c''4-2_"c-2"      s4
      c''4-3_"c-3"      s4
      c''4-4_"c-4"      s4
    }
    \paper {
      linewidth = 5.875 \in;
      indent    = 0.0;
    }
  }

@end lilypond

Dynamic marks are specified by using an identifier after a note:
`@code{c4-\ff}' (the dash is optional for dynamics: `@code{c4 \ff})'.  
The available dynamic marks are:
@code{\ppp}@keyindex{ppp},
@code{\pp}@keyindex{pp}, @code{\p}@keyindex{p}, @code{\mp}@keyindex{mp},
@code{\mf}@keyindex{mf}, @code{\f}@keyindex{f}, @code{\ff}@keyindex{ff},
@code{\fff}@keyindex{fff}, @code{\fff}@keyindex{ffff},
@code{\fp}@keyindex{fp}, @code{\sf}@keyindex{sf},
@code{\sff}@keyindex{sff}, @code{\sp}@keyindex{sp},
@code{\spp}@keyindex{spp}, @code{\sfz}@keyindex{sfz}, and
@code{\rfz}@keyindex{rfz}.


@example

  \textscript@keyindex{textscript} @var{text} @var{style}
@end example

Defines a text to be printed over or under a note.  @var{style} is a
string that may be one of @code{roman}, @code{italic}, @code{typewriter}, 
@code{bold}, @code{Large}, @code{large}, @code{dynamic} or @code{finger}.

You can attach a general textscript request using this syntax:

@quotation

@example 
c4-\textscript "6" "finger"
c4-\textscript "foo" "normal" 
@end example 

@end quotation

This is equivalent to `@code{c4-6 c4-"foo"}'.  


@cindex scripts

@example

  \script@keyindex{script} @var{alias}
@end example

Prints a symbol above or below a note.  The argument is a string
which points into the script-alias table defined in @file{script.scm}.
The scheme definitions specify whether the symbol follows notes into
the staff, dependence of symbol placement on staff direction, and a
priority for placing several symbols over one note.  Usually the
@code{\script}@keyindex{script} keyword is not used directly.  Various
helpful identifier definitions appear in @file{script.ly}.


@cindex slur

Slurs connects chords and try to avoid crossing stems.  A slur is
started with `@code{(}' and stopped with `@code{)}'.  The
starting `@code{(}' appears to the right of the first note in
the slur.  The terminal `@code{)}' appears to the left of the
first note in the slur.  This makes it possible to put a note in
slurs from both sides:

@lilypond[fragment,verbatim,center]
  f'()g'()a' [a'8 b'(] a'4 g'2 )f'4
@end lilypond


@cindex crescendo

A crescendo mark is started with @code{\cr}@keyindex{cr} and terminated
with @code{\rc}@keyindex{rc}.  A decrescendo mark is started with
@code{\decr}@keyindex{decr} and terminated with
@code{\rced}@keyindex{rced}.  There are also shorthands for these
marks.  A crescendo can be started with @code{\<}@keyindex{<} and a
decrescendo can be started with @code{\>}@keyindex{>}.  Either one can
be terminated with @code{\!}@keyindex{"!}.  Note that @code{\!}
must go before the last note of the dynamic mark whereas @code{\rc}
and @code{\rced} go after the last note.  Because these marks are
bound to notes, if you want to get several marks during one note, you
must use spacer notes.

@lilypond[fragment,verbatim,center]
  c'' \< \! c''   d'' \decr e'' \rced 
  < f''1 { s4 \< \! s2 \> \! s4 } >
@end lilypond


@example

  \spanrequest@keyindex{spanrequest} @var{startstop} @var{type}
@end example

Define a spanning request. The @var{startstop} parameter is either -1
(@code{\start}@keyindex{start}) or 1 (@code{\stop}@keyindex{stop}) and
@var{type} is a string that describes what should be started.
Supported types are @code{crescendo}, @code{decrescendo},
@code{beam}, @code{slur}.  This is an internal command.  Users should
use the shorthands which are defined in the initialization file
@file{spanners.ly}.

You can attach a (general) span request to a note using

@lilypond[fragment,verbatim,center]
  c'4-\spanrequest \start "slur"
  c'4-\spanrequest \stop "slur"
@end lilypond

The slur syntax with parentheses is a shorthand for this.



@cindex tremolo marks

@node stem tremolo, , ,  Reference Manual

Tremolo marks can be printed on a single note by adding
`@code{:}[@var{length}]' after the note.  The length must be at
least 8.  A @var{length} value of 8 gives one line across
the note stem.  If the length is omitted, then the last value is
used, or the value of the @code{tremoloFlags}@indexcode{tremoloFlags} property if there was
no last value.

@lilypond[verbatim,fragment,center]
  c'2:8 c':32
@end lilypond



@node Compound music expressions, , ,  Reference Manual
@section Compound music expressions

@cindex compound music expressions

Music expressions are compound data structures.  You can nest music
expressions any way you like.  This simple example shows how three
chords can be expressed in two different ways:

@lilypond[fragment,verbatim,center]
  \notes \context Staff {
    \cadenzaOn
    <a c'> <b  d' > <c' e'>
    < { a b  c' } { c' d' e' } >
  }
@end lilypond

@cindex context selection
@c @keyindex{context}

@example
  \context @var{contexttype} [= @var{contextname}] @var{musicexpr}
@end example

Interpret @var{musicexpr} within a context of type @var{contexttype}. 
If the context does not exist, it will be created.  The new context
can optionally be given a name.  

@cindex input modes

@cindex mode switch

Mode switching keywords form compound music expressions: @code{\notes}
@keyindex{notes} @var{musicexpr}, @code{\chords} @keyindex{chords}
@var{musicexpr}, and @code{\lyrics} @keyindex{lyrics} @var{musicexpr}. 
These expressions do not add anything to the meaning of their
arguments.  They are just a way to indicate that the arguments should
be parsed in indicated mode.  See @ref{Lexical modes} for more
information on modes.

@cindex sequential music



@example

  \sequential@keyindex{sequential}
    @code{@{} @var{musicexprlist} @code{@}}
@end example

This means that list should be played or written in sequence, i.e.,
the second after the first, the third after the second.  The duration
of sequential music is the the sum of the durations of the elements. 
There is a shorthand, which leaves out the keyword:

@example

  @code{@{} @var{musicexprlist} @code{@}}
@end example



@cindex simultaneous music

@indexcode{<}
@indexcode{>}

@example

  \simultaneous@keyindex{simultaneous}
    @code{@{} @var{musicexprlist} @code{@}}
@end example

It constructs a music expression where all of its arguments start at
the same moment.  The duration is the maximum of the durations of the
elements.  The following shorthand is a common idiom:

@example

  @code{<} @var{musicexprlist} @code{>}
@end example

If you try to use a chord as the first thing in your score, you might
get multiple staffs instead of a chord.

@lilypond[verbatim,center]
  \score {
    \notes <c''4 e''>
    \paper {
      linewidth = -1.;
    }
  }
@end lilypond

This happens because the chord is interpreted by a score context.
Each time a note is encountered a default Voice context (along with a
Staff context) is created.  The solution is to explicitly instantiate
a Voice context:

@lilypond[verbatim,center]
  \score {
    \notes\context Voice <c''4 e''>
    \paper {
      linewidth = -1.;
    }
  }
@end lilypond



@cindex relative pitch specification

@node relative, , , Reference Manual

It is easy to get confused by octave changing marks and accidentally
putting a pitch in the wrong octave.  A much better way of entering a
note's octave is `the relative octave' mode.

@example

  \relative@keyindex{relative} @var{startpitch} @var{musicexpr}
@end example

The octave of notes that appear in @var{musicexpr} are calculated as
follows: If no octave changing marks are used, the basic interval
between this and the last note is always taken to be a fourth or
less.@footnote{The interval is determined without regarding
accidentals.  A @code{fisis} following a @code{ceses} will be put above
the @code{ceses}.}  The octave changing marks `@code{'}' and `@code{,}'
can then be added to raise or lower the pitch by an extra octave. 
Upon entering relative mode, an absolute starting pitch must be
specified that will act as the predecessor of the first note of
@var{musicexpr}.

Entering scales is straightforward in relative mode.

@lilypond[fragment,verbatim,center]
  \relative c' {
    c d e f g a b c c,
  }
@end lilypond

And octave changing marks are used for intervals greater than a fourth.

@lilypond[fragment,verbatim,center]
  \relative c'' {
    c g c f, c' a, e'' }
@end lilypond

If the preceding item is a chord, the first note of the chord is used
to determine the first note of the next chord.  But other notes
within the second chord are determined by looking at the immediately
preceding note.

@lilypond[fragment,verbatim,center]
  \relative c' {
    c <c e g> 
    <c' e g>
    <c, e' g>
  }
@end lilypond 

The pitch after the @code{\relative} contains a notename.  To parse
the pitch as a notename, you have to be in note mode, so there must
be a surrounding @code{\notes}@keyindex{notes} keyword (which is not
shown here).

The relative conversion will not affect @code{\transpose} or
@code{\relative} sections in its argument.  If you want to use
relative within transposed music, you must place an additional
@code{\relative} inside the @code{\transpose}.

It is strongly recommended to use relative pitch mode: less work,
less error-prone, and more readable.



Chord names are a way to generate simultaneous music expressions that
correspond with traditional chord names.  It can only be used in
Chord mode (see section @ref{Lexical modes}).

@example

  @var{tonic}[@var{duration}][@code{-}@var{modifiers}][@code{^}@var{subtractions}][@code{/}@var{inversion}][@code{/+}@var{bass}].
@end example

@var{tonic} should be the tonic note of the chord, and @var{duration}
is the chord duration in the usual notation.  There are two kinds of
modifiers.  One type is @emph{chord additions}, which are obtained by
listing intervals separated by dots.  An interval is written by its
number with an optional `@code{+}' or `@code{-}' to indicate raising or
lowering by half a step.  Chord additions has two effects: It adds
the specified interval and all lower odd numbered intervals to the
chord, and it may lower or raise the specified interval.  Intervals
must be separated by a dot (`@code{.}').

@quotation

@lilypond[fragment,verbatim]
\transpose c'' {
  \chords {
    c1  c:3-       c:7     c:8
    c:9 c:9-.5+.7+ c:3-.5- c:4.6.8
  }
}

@end lilypond
@end quotation

The second type of modifier that may appear after the `@code{:}' is a
named modifier.  Named modifiers are listed in the file
@file{chord-modifiers.ly}.  The available modifiers are `@code{m}' and
`@code{min}' which lower the 3rd half a step, `@code{aug}@indexcode{aug}' which
raises the 5th, `@code{dim}@indexcode{dim}' which lowers the 5th,
`@code{maj}@indexcode{maj}' which adds a raised 7th, and `@code{sus}@indexcode{sus}'
which replaces the 5th with a 4th.

@quotation

@lilypond[fragment,verbatim]
\transpose c'' {
  \chords {
    c1:m c:min7 c:maj c:aug c:dim c:sus
  }
}

@end lilypond
@end quotation
 

Chord subtractions are used to eliminate notes from a chord.  The
notes to be subtracted are listed after a `@code{^}' character,
separated by dots.

@lilypond[fragment,verbatim,center]
  \transpose c'' {
    \chords {
      c1^3 c:7^5.3 c:8^7
    }
  }
@end lilypond 

Chord inversions can be specified by appending `@code{/}@indexcode{/}' and
the name of a single note to a chord.  This has the effect of
lowering the specified note by an octave so it becomes the lowest
note in the chord.  If the specified note is not in the chord, a
warning will be printed.

@lilypond[fragment,verbatim,center]
  \transpose c''' {
    \chords {
      c1 c/e c/g c:7/e
    }
  }

@end lilypond 

Bass notes can be added by `@code{/+}@indexcode{/+}' and
the name of a single note to a chord.  This has the effect of
adding the specified note to the chord, lowered by an octave,
so it becomes the lowest note in the chord.

@lilypond[fragment,verbatim,center]
  \transpose c''' {
    \chords {
      c1 c/+c c/+g c:7/+b
    }
  }

@end lilypond 

Throughout these examples, chords have been shifted around the staff
using @code{\transpose}.

You should not combine @code{\relative} with named chords. 



@cindex tuplets

Tuplets are made out of a music expression by multiplying their
duration with a fraction.

@example

  \times@keyindex{times} @var{fraction} @var{musicexpr}
@end example

The duration of @var{musicexpr} will be multiplied by the fraction. 
In print, the fraction's denominator will be printed over the notes,
optionally with a bracket.  The most common tuplet is the triplet in
which 3 notes have the length of 2, so the notes are 2/3 of
their written length:

@lilypond[fragment,verbatim,center]
  g'4 \times 2/3 {c'4 c' c'} d'4 d'4
@end lilypond



@cindex grace notes

@example

  \grace@keyindex{grace} @var{musicexpr}
@end example

A grace note expression has duration 0; the next real note is
assumed to be the main note.

You cannot have the grace note after the main note, in terms of
duration, and main notes, but you can typeset the grace notes to the
right of the main note using the property
@code{graceAlignPosition}@indexcode{graceAlignPosition}.

When grace music is interpreted, a score-within-a-score is set up:
@var{musicexpr} has its own time bookkeeping, and you could (for
example) have a separate time signature within grace notes.  While in
this score-within-a-score, you can create notes, beams, slurs, etc.
Unbeamed eighth notes and shorter by default have a slash through the
stem.  This behavior can be controlled with the
@code{flagStyle}@indexcode{flagStyle} property.

@quotation

@lilypond[fragment,verbatim]
\relative c'' {
  \grace c8 c4 \grace { [c16 c16] } c4
  \grace { \property Grace.flagStyle = "" c16 } c4
}

@end lilypond
@end quotation

At present, nesting @code{\grace}@keyindex{grace} notes, e.g.

@example

  @code{\grace @{ \grace c32 c16 @} c4}
@end example

may result in run-time errors of LilyPond.  Since the meaning of such
a construct is unclear, we don't consider this a loss.  Similarly,
juxtaposing two @code{\grace} sections is syntactically valid, but
makes no sense and may cause runtime errors.

Ending a staff or score with grace notes may also generate a run-time
error, since there will be no main note to attach the grace notes to.



@cindex repeats

@node Repeats, , , Reference Manual

In order to specify repeats, use the @code{\repeat}@keyindex{repeat}
keyword.  Since repeats look and sound differently when played or
printed, there are a few different variants of repeats.

@table @samp
  @item unfolded  
    Repeated music is fully written (played) out.  Useful for MIDI
    output.

  @item volta  
    This is the normal notation: Repeats are not written out, but
    alternative endings (voltas) are printed, left to right.

  @item folded  
    Alternative endings are written stacked, which is useful for
    lyrics.
@end table  

The syntax for repeats is

@example

  \repeat @var{variant} @var{repeatcount} @var{repeatbody}
@end example

If you have alternative endings, you may add

@example

  \alternative@keyindex{alternative}
    @code{@{} @var{alternative1}
            @var{alternative2}
            @var{alternative3} @dots{} @code{@}}
@end example

where each @var{alternative} is a Music expression.

Normal notation repeats are used like this:

@quotation

@lilypond[fragment,verbatim]
  c'1
  \repeat volta 2 { c'4 d' e' f' }
  \repeat volta 2 { f' e' d' c' }

@end lilypond
@end quotation

With alternative endings:

@quotation

@lilypond[fragment,verbatim]
  c'1
  \repeat volta 2 {c'4 d' e' f'} 
  \alternative { {d'2 d'} {f' f} }

@end lilypond
@end quotation

Folded repeats look like this:@footnote{Folded repeats offer little
more over simultaneous music.  However, it is to be expected that
more functionality -- especially for the MIDI backend -- will be
implemented.}

@quotation

@lilypond[fragment,verbatim]
  c'1
  \repeat fold 2 {c'4 d' e' f'} 
  \alternative { {d'2 d'} {f' f} }

@end lilypond
@end quotation

@quotation

@lilypond[fragment,verbatim]
\context Staff {
  \relative c' {
    \partial 4;
    \repeat volta 2 { e | c2 d2 | e2 f2 | }
    \alternative { { g4 g g } { a | a a a a | b1 } }
  }
}

@end lilypond
@end quotation

If you don't give enough alternatives for all of the repeats, then
the first alternative is assumed to be repeated often enough to equal
the specified number of repeats.

@quotation

@lilypond[fragment,verbatim]
\context Staff {
  \relative c' {
    \repeat volta 3 { \partial 4; e | c2 d2 | e2 f2 | }
    \alternative { { g4 g g }
                   {\partial 1; e4 e e } 
                   {\partial 1; a a a a | b1 } }
  }
}

@end lilypond
@end quotation

It is possible to nest @code{\repeat}.  This is not entirely
supported: the notes will come be in the right places, but the repeat
bars will not.



@cindex transposition of pitches

@node transpose, , , Reference Manual

A music expression can be transposed with
@code{\transpose}@keyindex{transpose}.  The syntax is

@example

  \transpose @var{pitch} @var{musicexpr}
@end example

This means that middle C in @var{musicexpr} is transposed to
@var{pitch}.

@code{\transpose} distinguishes between enharmonic pitches: both
@code{\transpose cis'} or @code{\transpose des'} will transpose up half
a tone.  The first version will print sharps and the second version
will print flats.

@quotation

@lilypond[fragment,verbatim]
\context Staff {
  \clef "F";
  { \key e \major; c d e f }
  \clef "G";
  \transpose des'' { \key e \major; c d e f }
  \transpose cis'' { \key e \major; c d e f }
}

@end lilypond
@end quotation

If you want to use both @code{\transpose} and @code{\relative}, then
you must use @code{\transpose} first.  @code{\relative} will have no
effect music that appears inside a @code{\transpose}.



@cindex automatic lyric durations

If you have lyrics that are set to a melody, you can import the
rhythm of that melody into the lyrics using @code{\addlyrics}.
@keyindex{addlyrics} The syntax for this is

@example

  \addlyrics @var{musicexpr1 musicexpr2}
@end example

This means that both @var{musicexpr1} and @var{musicexpr2} are
interpreted, but that every non-command atomic music expression
(``every syllable'') in @var{musicexpr2} is interpreted using timing
of @var{musicexpr1}.

If the property @code{automaticMelismata}@indexcode{automaticMelismata} is set in the
context of @var{musicexpr1}, no lyrics will be put on slurred or tied
notes.

@quotation

@lilypond[verbatim,fragment]
\addlyrics
\transpose c'' {
  \property Voice.automaticMelismata = ##t
  c8 () cis d8. e16 f2
}
\context Lyrics \lyrics {
 do4 re mi fa }

@end lilypond
@end quotation

You should use a single rhythm melody, and single rhythm lyrics (a
constant duration is the obvious choice).  If you do not, you will get
undesired effects when using multiple stanzas:

@quotation

@lilypond[verbatim,fragment]
\addlyrics
\transpose c'' {
  c8 () cis d8. e16 f2
}
\context Lyrics \lyrics
< { do4 re mi fa }
  { do8 re mi fa } >

@end lilypond
@end quotation

It is valid (but probably not very useful) to use notes instead of
lyrics for @var{musicexpr2}.




@node Ambiguities, , ,  Reference Manual
@section Ambiguities

@cindex ambiguities

The grammar contains a number of ambiguities.@footnote{The authors
hope to resolve them at a later time.}

@itemize @bullet
  @item  The assignment

         @example 
foo = bar 
@end example 

       can be interpreted as making a string identifier @code{\foo}
       containing @code{"bar"}, or a music identifier @code{\foo}
       containing the syllable `bar'.

  @item  The assignment

         @example 
foo = -6 
@end example 

       can be interpreted as making an integer identifier
       containing -6, or a Request identifier containing the
       fingering `6' (with neutral direction).

  @item  If you do a nested repeat like

       @quotation

@example 
\repeat @dots{}
\repeat @dots{}
\alternative 
@end example 

       @end quotation

       then it is ambiguous to which @code{\repeat} the
       @code{\alternative} belongs.  This is the classic if-then-else
       dilemma.  It may be solved by using braces.

  @item  (an as yet unidentified ambiguity :-)
@end itemize



@node Notation conversion specifics, , ,  Reference Manual
@section Notation conversion specifics



@cindex automatic beam generation

@node autobeam, , ,  Reference Manual

By default, LilyPond will generate beams automatically.  This feature
can be disabled by setting the @code{Voice.noAutoBeaming}@indexcode{Voice.noAutoBeaming}
property to 1.  It can be overridden for specific cases by
specifying explicit beams.


A large number of Voice properties are used to decide how to generate
beams.  Their default values appear in @file{auto-beam-settings.ly}.
In general, beams can begin anywhere, but their ending location is
significant.  Beams can end on a beat, or at durations specified by
the @code{Voice.beamAutoEnd}@indexcode{Voice.beamAutoEnd} property.  To end beams every
quarter note, for example, you could set
@code{Voice.beamAutoEnd}@indexcode{Voice.beamAutoEnd} equal to `@code{"1/4"}'.  To end beams
at every three eighth notes you would set it to `@code{"3/8"}'.  The
same syntax can be used to specify beam starting points using
@code{Voice.beamAutoBegin}@indexcode{Voice.beamAutoBegin}.

To allow different settings for different time signatures, these
property names can start with `@code{time}@var{N}@code{_}@var{M}' to
restrict the definition to `@var{N}@code{/}@var{M}' time.  For example,
to specify beams ending only for 6/8 time you would use the
property @code{Voice.time6_8beamAutoEnd}.  To allow different endings
for notes of different durations, the duration can be tacked onto the
end of the property.  To specify beam endings for beams that contain
32nd notes, you would use @code{Voice.beamAutoEnd_32}.



@cindex chord names

@cindex chords

@cindex printing!chord names

For displaying printed chord names, use the @code{ChordNames}@indexcode{ChordNames}
and @code{ChordNameVoice}@indexcode{ChordNameVoice} contexts.  The chords may be entered
either using the notation described above, or directly using
simultaneous music.

@quotation

@lilypond[fragment,verbatim]
<
  \context ChordNames {
    \chords{a b c} \notes{<d f g>  <e g b>}
  }
  \context Staff \notes {
    a b c' d' e'
  }
>

@end lilypond
@end quotation

LilyPond examines chords specified as lists of notes to determine a
name to give the chord.  By default, LilyPond will not try to
identify chord inversions:

@lilypond[fragment,verbatim,center]
  <
    \context ChordNameVoice \notes {
      <e'1 g' c''>
    }
    \context Thread \notes {
      <e'1 g' c''>
    }
  >
@end lilypond

If you want inversions to be recognized, you must set the property
@code{ChordNames.chordInversion}@indexcode{ChordNames.chordInversion}:

@lilypond[fragment,verbatim,center]
  <
    \property Score.chordInversion = ##t
    \context ChordNameVoice \notes {
      <e'1 g' c''>
    }
    \context Thread \notes {
      <e'1 g' c''>
    }
  >
@end lilypond



@cindex lyrics

@cindex printing!lyrics

@node lyricprint, , ,  Reference Manual

Lyric syllables must be interpreted within a @code{Lyrics} context

@cindex context!Lyrics
 for printing them.

Here is a full example: 

@quotation

@lilypond[verbatim]
\score {
  <
    \notes \transpose c'' {
      c d e c | c d e c |
      e f g2 | e4 f g2 \bar "|.";
    }
    \context Lyrics \lyrics { 
      Va-4 der Ja- cob Va- der Ja- cob
      Slaapt gij nog?2 Slaapt4 gij nog?2
    }
  >
}

@end lilypond
@end quotation

You may want a continuous line after the syllables to show melismata. 
To achieve this effect, add a `@code{__}' lyric as a separate word
after the lyric to be extended.  This will create an extender, a line
that extends over the entire duration of the lyric.  This line will
run all the way to the start of the next lyric, so you may want to
shorten it by using a blank lyric (using `@code{_}').

@quotation

@lilypond[verbatim]
\score {
  <
    \notes \relative c'' {
      a4 () b () c () d | c () d () b () a | c () d () b () a
    }
    \context Lyrics \lyrics {
      foo1 __ | bar2. __ _4 | baz1 __
    }
  >
}

@end lilypond
@end quotation

     
If you want to have hyphens centered between syllables (rather than
attached to the end of the first syllable) you can use the special
`@code{-}@code{-}' lyric as a separate word between syllables.  This
will result in a hyphen which length varies depending on the space
between syllables, and which will be centered between the syllables. 
For example:

@quotation

@lilypond[verbatim]
\score {
  <
    \notes \transpose c'' {
      c d e c | c d e c |
      e f g2 | e4 f g2 \bar "|.";
    }
    \context Lyrics \lyrics {
      Va4 -- der Ja -- cob | Va -- der Ja -- cob |
      Slaapt gij nog?2 | Slaapt4 gij nog?2
    }
  >
}

@end lilypond
@end quotation



@node Notation Contexts, , ,  Reference Manual
@section Notation Contexts

@cindex notation contexts

Notation contexts are objects that only exist during a run of
LilyPond.  During the interpretation phase of LilyPond, the Music
expression contained in a @code{\score} block is interpreted in time
order.  This is the order in which humans read, play, and write
music.

A context is an object that holds the reading state of the
expression; it contains information like

@itemize @bullet
  @item  What notes are playing at this point?
  @item  What symbols will be printed at this point?
  @item  In what style will they printed?
  @item  What is the current key signature, time signature, point within
       the measure, etc.?
@end itemize

Contexts are grouped hierarchically: A @code{Voice} context is
contained in a @code{Staff} context (because a staff can contain
multiple voices at any point), a @code{Staff} context is contained in
a @code{Score}, @code{StaffGroup}, or @code{ChoirStaff} context (because
these can all contain multiple staffs).

Contexts associated with sheet music output are called @emph{notation
contexts}, those for sound output are called playing contexts.

Contexts are created either manually or automatically.  Initially,
the top level music expression is interpreted by the top level
context (the @code{Score} context).  When a atomic music expression
(i.e. a note, a rest, @code{\bar}, or @code{\time} commands), a nested
set of contexts is created that can process these atomic expressions,
as in this example:

@example

  @example 
\score @{ \notes < c4 > @} 
@end example 

@end example

The sequential music, `@code{@{ c4 @}}' is interpreted by @code{Score}
context. When the note `@code{c4}' itself is interpreted, a set of
contexts is needed that will accept notes.  The default for this is a
@code{Voice} context, contained in a @code{Staff} context.  Creation of
these contexts results in the staff being printed.


@cindex context

You can also create contexts manually, and you probably have to do so
if you want to typeset complicated multiple part material.  If a
`@code{\context} @var{name} @var{musicexpr}' expression is encountered
during the interpretation phase, the @var{musicexpr} argument will be
interpreted with a context of type @var{name}.  If you specify a name,
the specific context with that name is searched.

If a context of the specified type and name can not be found, a new
one is created.  For example,

@quotation

@lilypond[verbatim]
\score {
  \notes \relative c'' {
    c4 <d4 \context Staff = "another" e4> f
  }
}

@end lilypond
@end quotation

In this example, the @code{c} and @code{d} are printed on the
default staff.  For the @code{e}, a context Staff called
`@code{another}' is specified; since that does not exist, a new
context is created.  Within @code{another}, a (default) Voice context
is created for the @code{e4}.  When all music referring to a
context is finished, the context is ended as well.  So after the
third quarter, @code{another} is removed.

Almost all music expressions inherit their interpretation context
from their parent.  In other words, suppose that the syntax for a
music expression is

@example

  \keyword @var{musicexpr1} @var{musicexpr2} @dots{}
@end example

When the interpretation of this music expression starts, the context
for @var{musicexpr1}, @var{musicexpr2}, etc. is that of the total
expression.

Lastly, you may wonder, why this:

@quotation

@example 
\score @{
  \notes \relative c'' @{
    c4 d4 e4
  @}
@} 
@end example 

@end quotation

doesn't result in this:

@lilypond[]

  \score {
    \notes \relative c'' {
      <c4> <d4> <e4>
    }
  }

@end lilypond

For the @code{c4}, a default @code{Staff} (with a contained
@code{Voice}) context is created.  After the @code{c4} ends, no
music refers to this default staff, so it would be ended, with the
result shown.  To prevent this inconvenient behavior, the context to
which the sequential music refers is adjusted during the
interpretation.  So after the @code{c4} ends, the context of the
sequential music is also the default @code{Voice} context. 
The @code{d4} gets interpreted in the same context
as @code{c4}.



These are the contexts supplied with the package.  They are defined
in the initialization file @file{ly/engraver.ly}.

@table @samp
@end table



Properties that are set in one context are inherited by all of the
contained contexts.  This means that a property valid for the
@code{Voice} context can be set in the @code{Score} context (for
example) and thus take effect in all @code{Voice} contexts.

Properties can be preset within the @code{\translator} block
corresponding to the appropriate context.  In this case, the syntax
is

@example

  @var{propname} @code{=} @var{value}
@end example

This assignment happens before interpretation starts, so a
@code{\property} expression will override any predefined settings.

The @code{\property} expression will create any property you specify.
There is no guarantee that a property will be used.  So if you spell
a property name wrong, there will be no error message.

The property settings are used during the interpretation phase.  They
are read by the LilyPond modules where interpretation contexts are
built of.  These modules are called @emph{translators}.  Translators for
notation are called @emph{engravers}, and translators for sound are
called @emph{performers}.

The precise result of a property is determined by the implementation
of the translator that reads them.  Therefore, the result of a
property can vary, since it is implementation and configuration
dependent.

In order to fully find out what properties are used, you must
currently search the source code for calls to @code{get_property}. 
The rest of the section is devoted to an (incomplete) overview of
available properties.

@mbinclude properties.itely

@node Notation output definitions, , ,  Reference Manual
@section Notation output definitions

@cindex output

@cindex notation output

@cindex output definition

@node paper, , ,  Reference Manual

The most important output definition is the @code{\paper} block, for
music notation.  The syntax is

@example

  @code{\paper @{} [@var{paperidentifier}] @var{items} @code{@}}
@end example

where each of the items is one of

@itemize @bullet
  @item  An assignment.  The assignment must be terminated by a
       semicolon.  

  @item  A context definition.  See section @ref{contextdefs} for
       more information on context definitions.

  @item
        FIXME now in SCM

        A margin shape declaration.  The syntax is

       @example

         \shape @var{indent1}@code{,} @var{width1}@code{,}
                      @var{indent2}@code{,} @var{width2} @dots{} @code{;}
       @end example

       @keyindex{shape}

       Each pair of @var{indent} and @var{width} values is a dimension
       specifying how far to indent and how wide to make the line. 
       The indentation and width of successive lines are specified by
       the successive pairs of dimensions.  The last pair of
       dimensions will define the characeristics of all lines beyond
       those explicitly specified.

  @item  \stylesheet  declaration.  Its syntax is

       @example
                \stylesheet @var{scm}
       @end example


        See font.scm for details of @var{scm} 
@end itemize



@cindex changing font size and paper size

The Feta font provides musical symbols at six different sizes.  These
fonts are 11 point, 13 point, 16 point, 20 point,
23 point, and 26 point.  The point size of a font is the
height of the five lines in a staff when displayed in the font.

Definitions for these sizes are the files @file{paperSZ.ly}, where
@code{SZ} is one of 11, 13, 16, 20, 23 and 26.  If you include
any of these files, the identifiers @code{paper_eleven},
@code{paper_thirteen}, @code{paper_sixteen}, @code{paper_twenty},
@code{paper_twentythree}, and @code{paper_twentysix} are defined
respectively.  The default @code{\paper} block is also set.

To change the paper size, you must first set the
@code{papersize}@indexcode{papersize} variable at top level.  Set it to the strings
@code{a4}, @code{letter}, or @code{legal}.  After this specification,
you must set the font as described above.  If you want the default
font, then use the 20 point font.  The new paper size will not
take effect if the font is not loaded and selected afterwards.  Paper
size selection works by loading a file named after the paper size you
select.



@cindex paper variables

@node Paper variables, , ,  Reference Manual

There is a large number of paper variables that are used to control
details of the layout.  These variables control the defaults for the
entire score.  Usually, they do not have to be changed; they are by
default set to values that depend on the font size in use.  The
values are used by the graphic objects while formatting the score;
they are therefore implementation dependent.  Most variables are
accompanied by documentation in the initalization file
@file{params.ly} or @file{paperSZ.ly}, where @code{SZ} is the staff
height in points.

Nevertheless, here are some variables you may want to use or change:

@table @samp
  @item @code{indent}@indexcode{indent}  
    The indentation of the first line of music.

  @item @code{staffspace}@indexcode{staffspace}
    The distance between two staff lines, calculated from the center
    of the lines.  You should use either this or @code{rulethickness}
    as a unit for distances you modify.
  
  @item @code{linewidth}@indexcode{linewidth}  
    Sets the width of the lines.  If set to -1.0, a single
    unjustified line is produced.

  @item @code{textheight}@indexcode{textheight}  
    Sets the total height of the music on each page. Only used by
    ly2dvi.

  @item @code{interscoreline}@indexcode{interscoreline}  
    Sets the spacing between the score lines. Defaults to 16 pt.

  @item @code{interscorelinefill}@indexcode{interscorelinefill}  
    If set to a positive number, the distance between the score 
    lines will stretch in order to fill the full page. In that
    case @code{interscoreline} specifies the minimum spacing.
    Defaults to 0.

  @item @code{stafflinethickness}@indexcode{stafflinethickness}  
    Determines the thickness of staff and bar lines. 
@end table


@node contextdefs, , ,  Reference Manual

@cindex context definition

A notation contexts is defined by the following information

@enumerate i
  @item  A name.

  @item  The LilyPond modules that do the actual conversion of music to
       notation.  Each module is a so-called
       @emph{engraver}
@cindex engraver
.

  @item  How these modules should cooperate, i.e. which ``cooperation
       module'' should be used.  This cooperation module is a special
       type of engraver.

  @item  What other contexts the context can contain,

  @item  What properties are defined.
@end enumerate

A context definition has this syntax:

@example

  \translator @code{@{}
                      @var{translatorinit} @var{translatormodifierlist}
                    @code{@}}
@end example

@var{translatorinit} can be an identifier or of the form

@example

  \type @var{typename} @code{;}
@end example

@var{typename} is one of

@table @samp
  @item @code{Engraver_group_engraver}@indexcode{Engraver_group_engraver}  
    The standard cooperation engraver.

  @item @code{Score_engraver}@indexcode{Score_engraver}  
    This is cooperation module that should be in the top level context.

  @item @code{Grace_engraver_group}@indexcode{Grace_engraver_group}  
    This is a special cooperation module (resembling
    @code{Score_engraver}) that is used to created an embedded
    `miniscore'.
@end table 

@var{translatormodifierlist} is a list of items where each item is
one of

@itemize @bullet
  @item  @code{\consists} @var{engravername} @code{;}  
    Add @var{engravername} to the list of modules in this context. 
  The order of engravers added with @code{\consists} is
    significant.
  
  @item  @code{\consistsend} @var{engravername} @code{;}  
    Analogous to @code{\consists}, but makes sure that
    @var{engravername} is always added to the end of the list of
    engravers.

    Some engraver types need to be at the end of the list; this
    insures they are put there, and stay there, if a user adds or
    removes engravers.  This command is usually not needed for
    end-users.
    
  @item  @code{\accepts} @var{contextname} @code{;}  
    Add @var{contextname} to the list of  context this context can
    contain.  The first listed context the context to create by
    default.
  
  @item  @code{\remove} @var{engravername} @code{;}  
    Remove a previously added (with @code{\consists}) engraver.
  
  @item  @code{\name} @var{contextname} @code{;}  
    This sets name of the context, e.g. @code{Staff}, @code{Voice}.  If
    the name is not specified, the translator won't do anything.

  @item  @var{propname} @code{=} @var{value} @code{;}  
    A property assignment.  It is allowed to use reals for
    @var{value}.
@end itemize

In the @code{\paper} block, it is also possible to define translator
identifiers.  Like other block identifiers, the identifier can only
be used as the very first item of a translator.  In order to define
such an identifier outside of @code{\score}, you must do

@quotation

@example 
\paper @{
  foo = \translator @{ @dots{} @}
@}
\score @{
  \notes @{
    @dots{}
  @}
  \paper @{
    \translator @{ \foo @dots{} @}
  @}
@} 
@end example 

@end quotation


@cindex paper types, engravers, and pre-defined translators

Some pre-defined identifiers can simplify modification of
translators.  The pre-defined identifiers are:

@table @samp
  @item @code{StaffContext}@indexcode{StaffContext}  
    Default Staff context. 

  @item @code{RhythmicStaffContext}@indexcode{RhythmicStaffContext}  
    Default RhythmicStaff context. 

  @item @code{VoiceContext}@indexcode{VoiceContext}  
    Default Voice context.  

  @item @code{ScoreContext}@indexcode{ScoreContext}  
    Default Score context. 

  @item @code{ScoreWithNumbers}@indexcode{ScoreWithNumbers}  
    Score context with numbering at the Score level.

  @item @code{BarNumberingStaffContext}@indexcode{BarNumberingStaffContext}  
    Staff context with numbering at the Staff level.

  @item @code{HaraKiriStaffContext}@indexcode{HaraKiriStaffContext}  
    Staff context that does not print if it only contains rests. 
    Useful for orchestral scores.@footnote{Harakiri, also called
    Seppuku, is the ritual suicide of the Samourai.}

  @item @code{OrchestralPartStaffContext}@indexcode{OrchestralPartStaffContext}

  @item @code{OrchestralScoreContext}@indexcode{OrchestralScoreContext}
@end table

Using these pre-defined values, you can remove or add items to the
translator:

@quotation

@example 
\paper @{
  \translator @{
    \StaffContext
    \remove Some_engraver;
    \consists Different_engraver;
  @}
@} 
@end example 

@end quotation

      
@node Sound output, , ,  Reference Manual
@section Sound output



The MIDI block is analogous to the paper block, but it is simpler.
The @code{\midi} block can contain:
@cindex MIDI block

@itemize @bullet
  @item  a @code{\tempo} definition
  @item  context definitions
@end itemize

Assignments in the @code{\midi} block are not allowed.



@cindex context definition

Context definitions follow precisely the same syntax as within the
\paper block.  Translation modules for sound are called performers.
The contexts for MIDI output are defined in @file{ly/performer.ly}.



@cindex MIDI instrument names

@node midilist, , , Reference Manual

The MIDI instrument name is set by the
@code{Staff.midiInstrument}@indexcode{Staff.midiInstrument} property or,
if that property is not set, the
@code{Staff.instrument}@indexcode{Staff.instrument} property.  The
instrument name should be chosen from the following list.  If the
selected string does not exactly match, then LilyPond uses the default
piano.

@c @quotation

@example 
"acoustic grand"            "contrabass"           "lead 7 (fifths)"
"bright acoustic"           "tremolo strings"      "lead 8 (bass+lead)"
"electric grand"            "pizzicato strings"    "pad 1 (new age)"
"honky-tonk"                "orchestral strings"   "pad 2 (warm)"
"electric piano 1"          "timpani"              "pad 3 (polysynth)"
"electric piano 2"          "string ensemble 1"    "pad 4 (choir)"
"harpsichord"               "string ensemble 2"    "pad 5 (bowed)"
"clav"                      "synthstrings 1"       "pad 6 (metallic)"
"celesta"                   "synthstrings 2"       "pad 7 (halo)"
"glockenspiel"              "choir aahs"           "pad 8 (sweep)"
"music box"                 "voice oohs"           "fx 1 (rain)"
"vibraphone"                "synth voice"          "fx 2 (soundtrack)"
"marimba"                   "orchestra hit"        "fx 3 (crystal)"
"xylophone"                 "trumpet"              "fx 4 (atmosphere)"
"tubular bells"             "trombone"             "fx 5 (brightness)"
"dulcimer"                  "tuba"                 "fx 6 (goblins)"
"drawbar organ"             "muted trumpet"        "fx 7 (echoes)"
"percussive organ"          "french horn"          "fx 8 (sci-fi)"
"rock organ"                "brass section"        "sitar"
"church organ"              "synthbrass 1"         "banjo"
"reed organ"                "synthbrass 2"         "shamisen"
"accordion"                 "soprano sax"          "koto"
"harmonica"                 "alto sax"             "kalimba"
"concertina"                "tenor sax"            "bagpipe"
"acoustic guitar (nylon)"   "baritone sax"         "fiddle"
"acoustic guitar (steel)"   "oboe"                 "shanai"
"electric guitar (jazz)"    "english horn"         "tinkle bell"
"electric guitar (clean)"   "bassoon"              "agogo"
"electric guitar (muted)"   "clarinet"             "steel drums"
"overdriven guitar"         "piccolo"              "woodblock"
"distorted guitar"          "flute"                "taiko drum"
"guitar harmonics"          "recorder"             "melodic tom"
"acoustic bass"             "pan flute"            "synth drum"
"electric bass (finger)"    "blown bottle"         "reverse cymbal"
"electric bass (pick)"      "skakuhachi"           "guitar fret noise"
"fretless bass"             "whistle"              "breath noise"
"slap bass 1"               "ocarina"              "seashore"
"slap bass 2"               "lead 1 (square)"      "bird tweet"
"synth bass 1"              "lead 2 (sawtooth)"    "telephone ring"
"synth bass 2"              "lead 3 (calliope)"    "helicopter"
"violin"                    "lead 4 (chiff)"       "applause"
"viola"                     "lead 5 (charang)"     "gunshot"
"cello"                     "lead 6 (voice)" 
@end example 

@c @end quotation



@node Pre-defined Identifiers, , ,  Reference Manual

@section Pre-defined Identifiers

@cindex pre-defined identifiers


Various identifiers are defined in the initialization files to
provide shorthands for some settings.  Most of them are in
@file{ly/declarations.ly}.

@table @samp
  @item @code{\break}@keyindex{break}  
    Force a line break in music by using a large argument for the
    keyword @code{\penalty}.

  @item @code{\nobreak}@keyindex{nobreak}  
    Prevent a line break in music by using a large negative argument
    for the keyword @code{\penalty}.

  @item @code{\normalkey}@keyindex{normalkey}  
    Select normal key signatures where each octave has the same key
    signature.  This sets the @code{Staff.keyoctaviation} property.

  @item @code{\shiftoff}@keyindex{shiftOff}  
    Disable horizontal shifting of note heads that collide. 

  @item @code{\shiftOn}@keyindex{shiftOn}  
    Enable note heads that collide with other note heads to be
    shifted horiztonally.

  @item @code{\slurBoth}@keyindex{slurBoth}  
    Allow slurs to be above or below notes.

  @item @code{\slurDown}@keyindex{slurDown}  
    Force slurs to be below notes.

  @item @code{\slurUp}@keyindex{slurUp}  
    Force slurs to be above notes.

  @item @code{\specialkey}@keyindex{specialkey}  
    Allow key signatures do differ in different octaves.  This sets
    the @code{Staff.keyoctaviation} property.

  @item @code{\stemBoth}@keyindex{stemBoth}  
    Allow stems, beams, and slurs to point either upwards or
    downwards, decided automatically by LilyPond.

  @item @code{\stemdown}@keyindex{stemdown}  
    Force stems, beams, and slurs to point down.

  @item @code{\stemUp}@keyindex{stemUp}  
    Force stems, beams and slurs to point up.

@end table

@node  Grobs, , , Reference Manual
@section Grobs

This section is about Grobs (short for Graphical Objects), which are
formatting objects used to create  the final output. This material is
normally the domain of LilyPond gurus, but occasionally,  a normal user
also has to deal with grobs.

The most simple interaction with Grobs are when you use
@code{\override}:

@example
        \property Voice.Stem \override #'direction = #1
@end example

This piece of lily input causes all stem objects to be stem-up
henceforth.  In effect, you are telling lilypond to extend the defintion
of the "Stem" grob with the setting @code{direction := 1}.  Of course
there are many more ways of customizing Lily output, and since most of
them involve Grobs in some form, this section explains some details of
how grobs work.

@menu
* What is a grob?::
* Callbacks::
* Setting grob properties::
* Items and Spanners::
* Pointer substitution::
@end menu

@node What is a grob?, , , Grobs

All grobs have an X and Y-position on the page.  These X and Y positions
are stored in a relative format, so they can easily be combined by
stacking them, hanging one grob to the side of another, and coupling
them into a grouping-grob.

Each grob has a reference point, or parent: the position of a grob is
stored relative to that reference point. For example the X-reference
point of a staccato dot usually is the note head that it applies
to. Whenever the note head is moved, the staccato dot moves along
automatically.

If you keep following offset reference points, you will always end up at
the root-object. This root object is called @code{Line_of_score}
@ref{(lilypond-internals)Element Line_of_score}, and it represents a
system (ie. a line of music).

All grobs carry a set of grob-properties.  In the Stem example above,
the property @code{direction} is set to value @code{1}.  The function
that draws the symbol (@code{Stem::brew_molecule}) uses the value of
@code{direction} to determine how to print the stem and the flag.  The
appearance of a grob is determined solely by the values of its
properties.

Often, a grob also is associated with a symbol. On the other hand, Some
grobs do not print any symbols, but take care of grouping objects. For
example, there is a separate grob that stacks staffs vertically, so they
are not printed in overstrike. The NoteCollision @ref{(lilypond-internals)Element
NoteCollision} is another example of an abstract grob.  It only moves
around chords, but doesn't print anything.

A complete list of grob types is found in @ref{(lilypond-internals)Elements}

Grobs are created in the "Interpreting music" phase, by things in
LilyPond called engravers.  In this phase of the translation, a load of
grobs are created, and they are linked into a giant network of objects.
This network of grobs forms the "specification" of the print
problem. This problem is then solved: configurations, directions,
dimensions, line breaks, etc.  are calculated. Finally,   the printing
description in the form of Molecules (@ref{Molecule})  is extracted from
the network. These are then dumped into the output file

@node Callbacks, , , Grobs

Offsets of grobs are relative to a parent reference point. Most
positions are not known when an object is created, so these are
calculated as needed. This is done by adding a callback for a specific
direction.

Suppose you have the following code in a .ly file.
@example
        #(define (my-callback gr axis)
                (*  2.0 (get-gr-property grob 'direction))
        )

....

        \property Voice.Stem \override #'Y-offset-callbacks = #(list
                        my-callback)
@end example

When the Y-offset of a Stem object is needed, LilyPond will
automatically execute all callbacks for that object. In this case, it
will find @code{my-callback}, and execute that. The result is that the
stem is translated by two staff spaces in its direction.

(note: Y-offset-callbacks is also a property) 


Offset callbacks can be stacked, ie.

@example
        \property .... \override #'Y-offset-callbacks = #(list
                callback1 callback2 callback3)

@end example

The callbacks will be executed in the order callback3 callback2
callback1. This is used for quantized positioning: the staccato dot is
above or below a note head, and it must not be on a staff-line.

To achieve this, for the staccato there are two callbacks: one callback
that positions the grob above or below the note head, and one callback
that rounds the Y-position of the grob to the nearest open space.

Similarly, the size of a grob are determined through callbacks, settable
with grob properties @code{X-extent-callback} and @code{Y-extent-callback}.
There can be only one extent-callback for each axis. No callback (value #f)
means: "empty in this direction". If you fill in a pair, that pair
hard-codes the extent in that coordinate.


@node Setting grob properties, , , Grobs

Grob properties are stored as GUILE association lists, with symbols as
keys.   From C++, element properties can be accessed using the functions

@example
  SCM  get_grob_property (SCM) const;
  void set_grob_property (const char * , SCM val);
  void set_immutable_grob_property (const char * , SCM val);
  void set_immutable_grob_property (SCM key, SCM val);  
  void set_grob_property (SCM , SCM val);  
  void set_grob_pointer (const char*, SCM val);
  SCM  remove_grob_property (const char* nm);
@end example

In GUILE, LilyPond provides

@example
        ly-get-grob-property GROB SYMBOL
        ly-set-grob-property GROB SYMBOL VALUE
@end example

All lookup functions identify undefined properties with 
end-of-list (ie. @code{'()} in Scheme or @code{SCM_EOL} in C)

Properties are stored in two ways:
@itemize @bullet
@item mutable properties:
element properties that change from object to object. The storage of
these are private to a grob. Typically this is used to store lists of
pointers to other grobs

@item immutable properties:
element properties that are shared across different grobs of the same
type. The storage is shared, and hence it is read-only. Typically, this
is used to store function callbacks, and values for shared element
properties are read from @file{scm/element-description.scm}.
@end itemize

There are two ways to manually set grob properties.

You can change immutable grob properties. This is done with the
\override syntax:

@example
        \property Voice.Stem \override #'direction = #1
@end example

This will push the entry @code{'(direction . 1)} on the immutable
property list for stems, in effect overriding the setting from
@file{scm/element-description.scm}. This can be undone by 

@example
        \property Voice.stem \revert #'direction
@end example

If you use this a lot, this gets old quickly. So we also have a
shorthand,

@example
        \property Context.GrobType \set #'prop = #VAL
@end example

this does a @code{\revert} followed by a @code{\override}

The second way is \outputproperty. This construct looks like

@example
        \context ContextName \outputproperty @var{pred} #@var{sym} = #@var{val}
@end example

In this case, in every grob that satisfies @var{pred}, the property
assignment @var{sym} = @var{val} is done.  For example

@example
        \outputproperty
                #(lambda (gr) (string? (ly-get-grob-property gr
                        'text)))
                #'extra-offset = #'(-1.0 . 0.0)
@end example

This shifts all elements that have a @code{text} property one staff
space to the left. This mechanism is rather clumsy to use, but it allows
you tweak any setting of any grob.

@node Items and Spanners, , , Grobs
@unnumberedsubsec Items and Spanners

Grobs can also be distinguished in their role in the horizontal spacing.
A lot of grobs define constraints on the spacing by their sizes. For
example, note heads, clefs, stems, and all other symbols with a fixed
shape.  These grobs form a subtype called @code{Item}.

Other grobs have a shape that depends on the horizontal spacing. For
example, slur, beam, tie, etc. These grobs form a subtype called
@code{Spanner}. All spanners have two span-points (these must be
@code{Item}s), one on the left and one on the right. The left bound is
also the X-reference point.

Some items need special treatment for line breaking. For example, a
clef is normally only printed at the start of a line (ie. after a line
break).  To model this, `breakable' items (clef, key signature, bar lines,
etc.) are copied twice. Then we have three versions of each breakable
item: one version if there is no line break, one version that is printed
before the line break (at the end of a system), one version that is
printed after the line break.

Whether these versions are visible and take up space, is determined by
the outcome of the visibility-lambda. This is a function taking a
direction (-1, 0 or 1) and returns a cons of booleans, signifying wether
this grob should be transparent and invisible.

@node Pointer substitution, , , Grobs
@unnumberedsubsec Pointer substitution


Symbols that cross line-breaks (such as slurs) cause some more
complications. When a  spanner crosses a line-break, then the spanner is
"broken into pieces", for every line that the spanner is in, a copy of
the grob is made. A substitution process redirects all grob-reference
so that spanner grob will only reference other grobs in the same line.

@node Molecule, , , Reference Manual

The objective of any typesetting system is to put ink on paper in the
right places. For LilyPond, this final stage is left to the TeX and the
printer subsystem. For lily, the last stage in processing a score is
outputting a description of what to put where.  This description roughly
looks like

@example
        PUT glyph AT (x,y)
        PUT glyph AT (x,y)
        PUT glyph AT (x,y) 
@end example

you merely have to look at the tex output of lily to see this.
Internally these instructions are encoded in Molecules:@footnote{At some
point LilyPond also contained Atom-objects, but they have been replaced
by Scheme expressions.}.  A molecule is an object that combines
dimension information (how large is this glyph ?) with
what-to-print-where.

Conceptually, Molecules can be constructed from Scheme code, by
translating a Molecule and by combining two molecules. In BNF notation:

@example
 Molecule = COMBINE Molecule Molecule
           | TRANSLATE Offset Molecule
           | GLYPH-DESCRIPTION
           ;
@end example

(refer to the C++ code for more details). All visible,
ie. non-transparent, grobs have a callback to create a Molecule. The
name of the property is @code{molecule-callback}, and its value should
be a Scheme function taking one argument (the grob) and returning a
Molecule.